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Even when happy, some people resist smiling. Or they cover their mouth with their hand. Their crooked teeth embarrass them.

That’s when you need to see an orthodontist.

Orthodontists are dentists with advanced training in making teeth move. They can realign crooked teeth into a straight, healthy smile.

It’s a transformation Gwen Henson saw recently when her 15-year-old son gleefully got his braces removed. That’s when she decided to treat herself to an unlikely 50th birthday present: her own set of braces.

“Getting braces was something I had thought about for years,” says Henson, an executive in Tempe, Ariz.

Her smile was only part of it. Henson also knew there are potential health issues when teeth begin shifting.

Henson is not alone. In the U.S., one in five orthodontic patients is an adult, according to the American Association of Orthodontists (AAO).

Here's what you should know if you're considering getting orthodontic work done.

What Do Orthodontists Do?

The top reason for seeing an orthodontist is the same for adults and kids - to treat malocclusion, or a “bad bite.”

Orthodontists help straighten teeth and improve your bite by correcting how your teeth fit together and how your jaws line up.

They use braces, trays (also known as aligners), and other appliances -- such as headgear, which attach around the head or neck to add more force to help make teeth move. They also use retainers to hold teeth in position.

General dentists often refer patients to orthodontists and sometimes medical doctors such as pediatricians do, too. That’s more likely to happen if a child “doesn’t like their teeth and is being teased about them,” says Michael B. Rogers, DDS, president of the AAO and an orthodontist in Augusta, Ga.

To become an orthodontist, someone must complete four years of dental school, then two to three years of specialized study in orthodontics.

Most general dentists can treat minor orthodontic problems and some do orthodontic work. But they’re more likely to refer complicated cases to an orthodontist.

Why See an Orthodontist

“Most patients see orthodontics as just straightening the teeth, but one of the most important factors is the way the bite fits together at the end of treatment,” says Alan R. Heller, DDS, an orthodontist with offices in Bethesda and Laurel, Md.

Crooked or crowded teeth, as well as overbites and underbites, can lead to tooth decay, gum disease, and even tooth loss. That’s because overlapping teeth can be tough to clean.

A bad bite also can cause problems when chewing and talking. Not to mention too much wear, grinding, and clenching.

Orthodontics has come a long way over the years. Primitive but well-designed orthodontic appliances have been found with Greek and Etruscan artifacts, Rogers says.

Stainless steel brackets and wires were introduced in 1927. Clear ceramic or porcelain brackets debuted in the 1970s. In 1999, Invisalign was introduced. It’s a series of clear trays that fit in the mouth and are changed every two weeks. Other tray aligners include ClearCorrect; Simpli5; and Red, White, and Blue.

Today, some braces are may be nearly invisible. Some have clear or tooth-colored brackets. Others are attached to the lingual (back side) of your teeth.

When to Go to an Orthodontist

The AAO recommends that children see an orthodontist no later than age 7, even if there are no problems. That’s because the jaw is still developing and it’s best to catch issues early.

“Most children go into orthodontic treatment when they are between 9 and 14 years old, but the average for girls is a little earlier,” Rogers says.

The typical adult patient might be 26 to 44 years old, but Rogers says he has also put braces on people in their 60s and 70s.

How long will treatment take? Orthodontists customize treatment for each patient. It usually takes one to three years.

Choosing an Orthodontist

To get her son’s teeth straightened, Henson asked family and friends for recommendations. She then interviewed three orthodontists. She decided to use her son’s doctor for her own braces because she liked her son’s treatment plan and the results - well, they made her smile.

The orthodontist also offered a family discount. And his office was convenient. That was a big plus for Henson, since she has appointments every six weeks.

Heller recommends asking how easy it is to schedule appointments. Whether a practice is right for you has a lot to do with the personality of the orthodontist and how good you feel when you’re there.

“The way the office runs and the way the patient is treated can vary quite a bit based on the practice’s philosophy, the personality of the doctor and how friendly the staff is,” Heller says.

Consultation First

Many orthodontists offer free or low-cost consultations. Rogers’ is 45 minutes long. It includes a panoramic X-ray that gives a full-mouth view, photographs, and a medical history.

Among other things, he measures how wide a patient can open her mouth and whether there’s jaw muscle tenderness or clicking, which may indicate grinding. He also measures the protrusion (how much teeth are jutting out) and crowding of the teeth.

Before they leave, patients get an estimate of treatment cost, length, and goals.

What You'll Pay

Costs for orthodontic work vary by doctor and region. Rogers charges about $5,880 for children and $6,380 for adults, although some may be lower or higher.

Heller says there is a range of prices “from one neighborhood to the next, as well as differences in the way some practices are run.” Some see as many as 100 patients a day. Other practices take fewer patients per day, including Heller’s, which sees 40 patients daily.

More expensive doesn’t always mean better. Go to an orthodontist who offers video games in the waiting room and lavish, high-dollar prizes? You might be paying more for flash than substance, Heller says.

Many orthodontists offer interest-free financing for clients with good credit. And most also offer financing through banks.

In 2010, 60% of all new patients had dental insurance that include orthodontic benefits, according to the AAO.

Ask if there’s a lifetime cap or maximum, or any age limits.

And remember: Just like dental insurance, orthodontic insurance is designed to cover just a portion of the fee, not all of it.

Loves What She Sees

Henson has a high-profile job as executive director of the Arizona Chapter of the National Speakers Association. She once worried what people would think when she showed up at events with braces. But “everybody was very supportive and encouraging," she says.

Today, when Henson looks in the mirror, she sees a shift in her teeth and her wellbeing.